How the memory stores information

06.05.2020

A research group led by Professor Dietmar Schmitz of Charité - Universitätsmedizin Berlin has pinpointed the area of the brain involved in transferring memory-associated information into long-term memory. The results have now been published in Nature Communications*.

The human brain constantly absorbs important information and data, collecting and storing it over long periods of time. We can repeatedly recall what has been previously learned. The hippocampus is the part of the brain responsible for these important processes. As we learn and create memories, information moves through temporal lobe structures – and through the hippocampus in particular – to be stored in the neocortex. The functions of the hippocampus are coupled to rhythms or so-called oscillations.

The team led by Prof. Dr. Dietmar Schmitz, Director of the Neuroscience Research Centre at Charité (NWFZ) and spokesperson for the NeuroCure Cluster of Excellence, has discovered that the transfer of memory-associated information from the hippocampus to the neocortex is mediated by a specific cortical area known as the retrosplenial cortex. This transfer occurs during high-frequency oscillations (so-called sharp wave ripples). Specific groups of nerve cells are involved in both structures. The findings indicate that these physiologically defined nerve cells play an important role in memory storage.

The scientists investigated how these sharp wave ripples (SPW-Rs) spread from the hippocampus into the cortex. By studying electrical currents in individual cells in the hippocampus and retrosplenial cortex that occur during ripple oscillation, they were able to discover that this interaction is topographically organized and layer-specific. Furthermore, they showed that the spread of hippocampal activity into the retrosplenial cortex is mediated by a specific neuronal subpopulation of hippocampal cells expressing the vesicular glutamate transporter 2 (VGlut2-expressing bursty neurons in the subiculum). Specific activation of these cells can induce ripple oscillations in the retrosplenial cortex, while deactivation strongly reduces the activity of the ripple equivalents in the retrosplenial cortex.

These results provide a better understanding of the hippocampal-cortical interaction and of how information that has been temporarily stored in the hippocampus is transferred to the neocortex. Although this is basic research, both regions being investigated are strongly involved in various memory disorders such as amnesia and Alzheimer's. Therefore, as Noam Nitzan, a Charité neuroscientist and the first author of the study says: "Better knowledge of these regions and networks can improve our understanding of memory loss." Next the researchers want to investigate how these memory-associated signals propagate from the retrosplenial cortex into the rest of the cerebral cortex, and thus into all areas connected to this region.